On the use of low-cost sensors to monitor urban air quality and assessment of their performance

The demand for high-resolution air quality data is growing in various fields, such as in climate change studies, health protection analyses, traffic management, etc. The use of modern Low-Cost Sensors (LCSs) creates an opportunity to collect data from different locations and to provide a detailed information at a reasonable cost. The number and type of commercially available sensors is increasing at a rapid pace, however, the performance of these sensors still remain poorly documented, as well as their accuracy, precision, reliability and duration. As suggested by Rai et al. (2017), to implement a large-scale sensor network and to use all data generated in a meaningful way, it is necessary to formulate standard guidelines to evaluate its performance in the short and long terms. The main problems are related to: calibration, stability, measurements in the field, interferences between gas and influence of temperature and relative humidity. In this work, we report the results of the tests carried out with the updated version of Smart Citizen Kits (SCK). SCKs are assemblages of LCSs that measure temperature, relative humidity, noise, light, NO2 and CO concentrations. In order to evaluate their performance in the field, the sensors are tested in real conditions in the city of Bologna during the winter (February 2018) and the summer (August-September 2017) as part of two extensive experimental campaigns. The repeatability of the sensors and the reproducibility are discussed under different meteorological conditions allowing us to formulate some guidelines for their implementation.